1. Field of the Invention
The present invention relates to a semiconductor device and manufacturing method, particularly to a semiconductor device including a thin dielectric film such as a gate dielectric film or capacitor dielectric film, and a manufacturing method of the device.
2. Description of the Related Art
In a semiconductor field such as LSI, miniaturization of a semiconductor device has heretofore been proceeded, but it has gradually become difficult to miniaturize the device. In an example of a MOS transistor, for instance, it has been increasingly difficult to reduce a gate leakage current and to decrease a physical film thickness of a gate dielectrics film.
To solve the problem, the use of a dielectric film having a higher permittivity than that of a silicon oxide film as a gate a dielectric film has been studied in order to inhibit increase of the gate leakage current involving the reduction of the physical film thickness of the gate dielectric film. As this type of the dielectric film, a dielectric film including silicon, oxygen, and nitrogen (hereinafter referred to as an SiON film) has been known.
A conventional process of the SiON film is as follows. First, the ultra-thin silicon oxide film (base oxide film) which is to be the SiON film is formed on a silicon substrate by thermal oxidation. Thereafter, the base oxide film is nitrided by plasma such as N2 plasma (nitrogen radical, nitrogen ion) to form the SiON film (e.g., see 2001 Symposium on VLSI Technology Digest of Technical Papers).
However, this type of conventional process of the SiON film has the following problem.
When the film thickness of the base oxide film is 2.5 nm or less, particularly 1.4 nm or less, at a nitriding time of the base oxide film by a nitrogen radical, and the like, oxygen replaced with nitrogen reaches an interface between the silicon substrate and base oxide film, the oxygen oxidizes the silicon substrate, and the physical film thickness of the SiON film increases. In other words, it is difficult to reduce the electrical film thickness of the SiON film.
Therefore, in the conventional process of the SiON film, even if the base oxide film is thinned, it is difficult to obtain an SiON film which has a desired small film thickness. This inhibits the miniaturization of the MOS transistor.